Ken:
My early '77 Spitfire has flat-top pistons, and I believe the CR is about
9.1:1. So the answer on milling the head appears to be "none". That would
be easy, since the pushrods wouldn't change. I also think this agrees with
other articles I have read, where .130" off the head resulted in 10.5 to
10.7 CR. There was also a good article on higher CR's in Spitfires awhile
back, dealing with properly setting the "squish" area (piston height, deck
height, and head gasket). I'm not sure if it was in Spit/GT6 magazine or
perhaps the Performance Research Industries "Edge" . The main thrust was
that squish area is more important than CR in controlling knock in the
engine, and milling the head does not always work as well as other options
(block, pistons, gasket, etc).
I'm not sure if it was standard practice to install flat-top pistons in the
'76-'77 1500's with the 9.1 CR, or if this was in fact the only difference
that accounted for the two different compression ratios in US 1500's over
the years....
Anybody else have thoughts on this??
-Mark
-----Original Message-----
From: Ken C [mailto:sdspitfire@worldnet.att.net]
Sent: Tuesday, October 24, 2000 4:33 PM
To: Spit Elist
Subject: 1500 Cylinder head
Spitlisters,
I have read or heard that the USA 1500cc cylinder head is 'deeper', and,
along with dished pistons, typically yields 7.5 to 1 compression. If flat
top pistons were used, any idea how much the head have to be milled in order
to bring everything up to 9.0 to 1 ? Would shorter push rods be needed ?
Ken C
'72 Spit
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